Revision 0 was all well and good, but the big clock IO panel PCB is relatively costly and won't find any usage in other projects. It serves mainly as a carrier for functionality that is already on modules (displays, light sensor). The fifteen LED/switch combinations might be split up in four identical sections of four switches each. There would be one module carrying only three switches. It would add cost in wiring and connectors, but this switch module could easier find usage in other projects. I would be able to use four of the five prototypes sent to me. These switch modules would also fit the 100mm square template of the PCB manufacturer. The different modules could then be mounted on a laser cut panel. A separate module would be needed for the rotary encoder. Buy them, not make.
- 4 Cherry MX switches with through hole LEDs
- 4 mounting holes 3.2mm
- 3pin JST XH (for LEDs) and 5pin JST XH (for switches). 8pin JST XH is uncommon on AliExpress.
- Add diode for switch control, as below. Diode might be replaced by 0ohm resistor for use with SX1509 or other keypad scanning engines.
The clock-io-panel uses matrix keyboard scanning. It requires 8 IO lines for 15 switches.
It's only added here as a reference, because it's a clever circuit: If not enough IO lines had been available, there would be an alternative approach:
This technique would require only 5 IO lines for 15 switches (max. 20 switches). The downside is that 5 diodes need to be added. This probably won't work with an SX1509 or similar which has a built in keypad scanning engine.